1. Field of the Invention
This invention relates generally to thermoplastic elastomer (TPE) materials. Thermoplastic elastomers are broadly defined as rubber-like materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials, yet have properties and performance similar to that of vulcanized rubber at service temperatures. The invention more specifically relates to thermoplastic elastomers which have been modified by the addition of a specific vinyl aromatic block copolymer. The compositions of the invention have improved adhesive properties with respect to polymeric substrates, and particularly with respect to engineering thermoplastics.
2. Description of the Prior Art
Blends which have a combination of both thermoplastic and elastic properties are generally obtained by combining a thermoplastic resin with an elastomeric material in a way such that the elastomer is intimately and uniformly dispersed as a discrete particulate phase within a continuous phase of the thermoplastic. Early work with the vulcanization of the elastomer phase is found in U.S. Pat. No. 3,037,954 which discloses static vulcanization, as well as dynamic vulcanization wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer is cured (crosslinked) while continuously mixing and shearing the blend.
U.S. Pat. No. 4,130,535 discloses thermoplastic elastomer compositions comprising thermoplastic olefin resins and olefin copolymer rubbers, prepared by dynamic vulcanization and wherein the rubber component is vulcanized to the extent that it is essentially insoluble in conventional rubber solvents. No details are given regarding adhesion properties of these compositions, but it is known that unmodified non-polar thermoplastic elastomers generally do not adhere to engineering resins.
Efforts to improve the adhesive properties of thermoplastic elastomers have been made through the incorporation of functionalized thermoplastic resins into the blends. One approach is described in U.S. Pat. No. 4,957,968 which discloses the addition of a functionalized polyolefin to improve adhesion to metals and polar polymers. U.S. Pat. No. 5,843,577 describes the incorporation of copolymers of polyamide and functionalized polyolefin to improve adhesion to polyamides. U.S. Pat. No. 5,852,118 discloses the addition of block copolymers of functionalized olefin, thermoplastic polyurethane, copolyester or copolyamide, and an isocyanate.
However, the problem of achieving good adhesion of thermoplastic elastomers to polymer substrates, and particularly to polar engineering thermoplastic substrates, either has not been overcome by these approaches or the techniques are too complex for practical application.